1. Field of the Invention
The present invention is directed to a process for preparing a crystalline silicate zeolite, and more particularly to a process for preparing a binder-free Zeolite Beta containing at least one highly dispersed noble metal. The present invention is specifically directed to a binder-free noble metal-containing Zeolite Beta crystalline silicate which has superior redispersion properties after having become deactivated.
2. Discussion of Prior Art
Shape-selective catalysis utilizing molecular sieves was first demonstrated by P. B. Weisz and V. J. Frilette in J. Phys. Chem., 64, page 302 (1960). Since then, the shape-selective catalytic properties of various zeolites have been extensively demonstrated. For example, N. Y. Chen and W. E. Garwood, in "Some Catalytic Properties of ZSM-5, a New Shape Selective Zeolite", Journal of Catalysis, 52, pages 453-458 (1978), described the shape-selectivity of ZSM-5. On the other hand, the use of zeolites as shape-selective supports for catalytic functions has received much less attention.
P. B. Weisz, V. J. Frilette, R. W. Maatman and F. B. Mower, in "Catalysis by Crystalline Aluminosilicates II. Molecular-Shape Reactions", Journal of Catalysis, 1, pages 307-312 (1962), described a shape-selective olefin hydrogenation catalyst comprising platinum incorporated in zeolite A. In U.S. Pat. No. 3,140,322 to V. J. Frilette and P. B. Weisz, a process is disclosed for hydrogenation using a platinum-containing zeolite. In U.S. Pat. No. 3,226,339 of V. J. Frilette and R. W. Maatman, a process is described for the preparation of a platinum-or palladium-containing zeolite catalyst. U.S. Pat. No. 3,575,045 to J. N. Miale discloses the use of platinum-entrained zeolite A for selective hydrogenation.
A catalyst and process for selectively hydrogenating ethylene in the presence of propylene utilizing a zeolite in conjunction with a hydrogenation metal is disclosed in U.S. Pat. No. 3,496,246. N. Y. Chen and P. B. Weisz, in "Molecular Engineering of Shape-Selective Catalysts", Kinetics and Catalysis, Chem. Eng. Prog. Symp., Ser. No. 73, Vol. 63, 1967, page 86, describes a platinum-catalyzed hydrogenation process employing a phosphine-poisoned, platinum-exchanged sodium mordenite zeolite.
An excellent summary of the art of metal-loaded zeolite catalysts and shape-selective catalysis is given in Zeolite Chemistry and Catalysts, J. A. Rabo, Ed., ACS Monograph 1 (1976). Of particular interest is Chapter 10, "Catalytic Properties of Metal-Containing Zeolites" by K. M. Minachev and Y. I. Isakov, and Chapter 12, "Shape-Selective Catalysis" by S. M. Csicsery.
Catalysts, such as ZSM-5 combined with a Group VIII metal, are described in U.S. Pat. No. 3,856,872 to Morrison. It is disclosed in this patent that the catalysts are preferably incorporated in a porous matrix, such as alumina. A Group VIII (hydrogenation) metal may then be added after incorporation with the zeolite in a matrix by such means as base-exchange or impregnation. In one embodiment, the metal is added in the form of chloroplatinic acid.
U.S. Pat. No. 4,188,282 discloses particularly preferred forms of noble metal-containing zeolites, such as ZSM-5, formed by the crystallization of the zeolite from a forming solution containing noble metal ions, such as those of platinum. U.S. Pat. No. 3,462,377 to Plank et al discloses the preparation of metal-containing zeolite catalysts in which the activity of the catalyst is enhanced by steaming.
British Pat. No. 1,189,850 discloses the preparation of a noble metal-containing zeolite catalyst, in which a metal-loaded ammonium zeolite, which has been manufactured by contacting zeolite material with ammonia and/or ammonium ions and which has been composited with one or more hydrogenation metals, is subjected to controlled oxidative calcination.
U.S. Pat. No. 4,312,790 to Butter et al discloses a method of preparing a noble metal-containing catalyst by incorporating a noble metal in a cationic form with a zeolite after crystallization of said zeolite, but prior to the final catalyst particle formation. The zeolite is calcined only after extrusion, i.e., after addition of the noble metal. Such catalysts have been found to be an improvement over those catalysts wherein the metal is incorporated during zeolite crystallization, or after extrusion. The catalyst thus produced also exhibits little hydrogenation-dehydrogenation activity.
The deactivation of noble metal-containing hydrocarbon conversion catalysts due to the deposition on the catalyst of carbonaceous residues is a well-known phenomenon which has received much attention in the technical and patent literature. The problem with regard to catalyst deactivation is particularly acute with respect to supported noble metal-containing catalysts employed in the reforming of naphtha feedstocks. Undesired metal migration and agglomeration can occur during preparation, calcination or oxidative regeneration of such catalysts, resulting in significant losses in catalyst properties, such as hydrogenation activity.
Numerous methods have been suggested by prior workers for the regeneration or rejuvenation of supported noble metal catalysts which have been deactivated. Regeneration can be defined as the process of removing carbonaceous materials from a catalyst generally by burning the catalyst in an oxygen atmosphere. Regeneration is most useful in those cases where the requirement on a noble metal bound to the catalyst is not severe, i.e., processes involving the catalytic processing of relatively clean hydrocarbon feedstocks. In those processes utilizing heavy crudes where the requirements on the catalyst are more severe, the deactivated catalyst must be rejuvenated. Rejuvenation is the process of ridding the catalyst of everything foreign to it and returning the catalyst to its original state. Rejuvenation also involves redispersing the metal that is on the catalyst. Rejuvenation generally requires a halogen step to redisperse to noble metal on the catalyst.
In U.S. Pat. Nos. 2,916,440; 3,243,384; 3,201,355; and 3,654,182, there are disclosed procedures utilizing gaseous mixtures containing oxygen and a halogen or halogen compound, particularly hydrogen chloride, for dissipating carbonaceous residue. In U.S. Pat. No. 3,378,419, there is disclosed a procedure for the rejuvenation of supported platinum catalysts involving (a) addition of halogen to the catalyst while in contact with the process feedstock, and (b) burning the coke deposits from the catalyst with an oxygen-containing, halogen-free regeneration gas.
It is also known in the art to rejuvenate platinum group metal-containing zeolite catalysts. Rejuvenation of noble metal-loaded zeolite catalysts requires certain procedural modifications because the metal must be returned in a dispersed form within the zeolite pores. U.S. Pat. No. 3,986,982 to Crowson et al treats deactivated platinum group metal-loaded zeolites by contacting them with a stream of an inert gas containing from 0.5 to 20 vol % of free oxygen and from 5 to 500 ppm volume of chlorine as Cl.sub.2, HCl, or an organic chlorine-containing material. The resulting catalyst is purged to remove residual oxygen and chlorine and then reduced in a stream of hydrogen at 200.degree. to 600.degree. C.
U.S. Pat. No. 4,359,400 to Landolt et al teaches a method of rejuvenating deactivated supported multi-metallic platinum-containing hydrocarbon conversion catalysts in the absence of oxygen or oxygen sources. The catalysts are contacted with an oxygen-containing gas at elevated temperatures followed by contact with a dry oxygen-free, hydrogen halide. The catalyst is then activated in the presence of chlorine gas and in the absence of oxygen or oxygen sources, such as water, followed by reduction with hydrogen. The catalysts, rejuvenatable by Landolt et al's method, may contain support materials comprising an aluminosilicate zeolite, such as naturally occurring or synthetic erionite, mordenite or faujasite.
U.S. Pat. No. 4,377,495 to Tse discloses rejuvenating sulfur-deactivated catalysts by contacting them with a hydrogen-rich gas, water, and a mixture of liquid chlorinated hydrocarbon and an oxygenated hydrocarbon, prior to coke burnoff.
Attempts have been made to increase the silica:alumina mole ratio of crystalline zeolites by removal of aluminum from the crystal structure with strong acids. The silica:alumina mole ratio of zeolites may also be increased by converting the parent zeolite at least partially to its hydrogen form, hydrolyzing the aluminum to aluminum hydroxide, and thereafter physically removing the displaced aluminum.
U.S. Pat. No. 3,442,795 discloses a process for preparing highly siliceous zeolite-type materials from crystalline aluminosilicates by means of a solvolysis, e.g., hydrolysis, followed by a chelation. In this process, the acid form of a zeolite is subjected to hydrolysis, to remove aluminum from the aluminosilicate. The aluminum can then be physically separated from the aluminosilicate by the use of complexing or chelating agents, such as ethylenediaminetetraacetic acid or carboxylic acid, to form aluminum complexes which are readily removable from the aluminosilicate. Ultra-high silicon-content zeolites and their preparation by the use of acid and complexing agents are disclosed in U.S. Pat. No. 4,093, 560. The method described in this patent is, however, applicable only to zeolites with a silica:alumina ratio of 2:1 to 6:1.
In U.S. Pat. No. 3,937,791, a method is described for removing alumina from a crystalline aluminosilicate. This method comprises heating the aluminosilicate to a temperature in the range between about 50.degree. and 100.degree. C., in the presence of a cationic form of chromium, in an aqueous solution of above 0.01N of a chromium salt of a mineral acid at a pH less than 3.5, so that the atomic ratio of chromium to aluminum is greater than 0.5.
A method for increasing the silica-to-alumina mole ratio of a crystalline aluminosilicate zeolite by contacting the zeolite with water at elevated temperature, and then treating to remove alumina from the crystal lattice, is disclosed in U.S. Pat. No. 3,591,488. Following the high temperature water treatment, amorphous alumina is removed from the zeolite material by contacting with a dilute mineral acid or an organic acid chelating agent.
In U.S. Pat. No. 3,640,681, framework aluminum is extracted from crystalline zeolites using acetylacetone as the extracting agent. Prior to contact with the acetylacetone, the zeolite must be rendered substantially cation-deficient and at least partially dehydroxylated. Other metals can be substituted for the extracted framework aluminum by contacting the zeolite with a metal acetylacetone.
The treatment of zeolites with gaseous chlorine compounds, such as Cl.sub.2 or HCl, to remove aluminum AlCl.sub.3, is described in DE-OS No. 2,510,740.
British Pat. No. 1,061,047 describes a method of removing alumina from certain zeolites, including stilbite and zeolites L and T, by treatment with mineral or organic acids. The zeolites which may be heated in this way have an initial silica:alumina ratio of at least 5:1. This technique was found, however, to be inapplicable with many zeolites, such as ZSM-5, especially those with higher silica:alumina ratios. In addition, certain zeolites, such as zeolites X and Y, lose an unacceptable large degree of crystallinity when treated with acid, although this may be mitigated by presence of a salt anion which is capable of combining with the aluminum, as reported in U.S. Pat. No. 3,691,099.
However, the prior art does not disclose an economical and efficient method of preparing a crystalline silicate Zeolite Beta of improved platinum redispersion characteristics.